Exhaust gas sensor and method of manufacture

Description

BACKGROUND

[0001] The present invention relates to exhaust gas sensors.

[0002] Exhaust gas sensors help assure that an optimum air to fuel ratio is maintained in combustion engines. Typically, exhaust gas sensors are located in automobiles to compare the oxygen content of the exhaust with the oxygen content of surrounding air. Feedback from the sensor controls the amount of fuel injected into the engine. Planar type sensors and thimble type sensors are two common types of exhaust gas sensors. Planar type sensors include a flat ceramic sensor element. Thimble type sensors include a thimble-shaped sensor element. The US 4 283 261 A discloses how to measure partial oxygen pressure in gases, particularly exhaust gases of automotive-type combustion engines, where solid electrolyte sensor elements are fixed in a holding structure of injection molded ceramic. Another document, US 2004/040843 A1 relates to a gas sensor determining at least one physical quantity of a gas, e.g., an exhaust gas of an internal combustion engine, and the gas sensor has a sensor element that is fixed in a housing of the gas sensor by a seal assembly. The DE 10 2005 020 792 A1 describes a sensor that has a sensor element carrying a contact surface which is contacted to a contact part for connection to an electrical connecting line; the contact part is accommodated in a contact holder made of electrically insulating material. Another document, WO 98/38505 A1 relates to a detector, specially one determining the oxygen content in exhaust gases of internal combustion motors, and to a method for the production thereof. The publication WO 01/34951 A2 discloses a terminal connector assembly that comprises a terminal support, a terminal, disposed at least partially within the terminal support, and a first insulator having a passage with an indentation adjacent to the terminal, and the terminal support. A gas sensor and a method of producing a gas sensor is also disclosed. Finally, the EP 0 520 528 A1 describes an improved sealing means that is provided for sealing a solid electrolyte ceramic body within a metal housing for use in an oxygen sensing device which is suitable for detecting the oxygen concentration within automotive exhaust gases emitted from an internal combustion engine.

SUMMARY

[0003] The invention provides a method of manufacturing an exhaust gas sensor as defined in claim 1 and an exhaust gas sensor as defined in claim 11.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Fig. 1 is a perspective view of an exhaust gas sensor embodying the present invention.

[0005] Fig. 2 is a cross-sectional view of the exhaust gas sensor shown in Fig. 1 taken along line 2-2 of Fig. 1.

[0006] Fig. 3 is a cross-sectional view of a subassembly of the exhaust gas sensor shown in Fig. 1 positioned within a mold fixture.

[0007] Fig. 4 is a partially exploded perspective view of the components of the exhaust gas sensor shown in Fig. 1.

DETAILED DESCRIPTION

[0008] Fig. 1 illustrates an exhaust gas sensor 10 of the present invention. The sensor 10 includes a sensor subassembly 14 and an exit lead or wire harness subassembly 18. The illustrated sensor subassembly 14, or short sensor assembly, includes a generally cylindrical metallic housing 22 configured to be threadably engaged with a threaded aperture of an exhaust pipe (not shown) or other component of an internal combustion engine used for automotive applications or non-automotive applications, such as motorcycles, snowmobiles, ATV's, lawnmowers, and the like.

[0009] Referring to Fig. 2, the illustrated sensor subassembly 14 also includes a ceramic material 26, a sensor element 30, a spacer 34, and a weld ring 38. The ceramic material 26 is molded to the housing 22 to encapsulate a middle portion of the sensor element 30 and to partially fill a bore 42 in the housing 22. During molding, the ceramic material 26 bonds to the housing 22 and the middle portion of the sensor element 30. In the illustrated construction, the ceramic material 26 is a MICAVER^® HT mica material available from Saint-Gobain Quartz S.A.S. of France. The ceramic material 26 abuts the spacer 34, which in the illustrated embodiment is a sintered steatite bushing positioned in the housing 22 to act as a thermal barrier between the hot exhaust gases (e.g., greater than 700 degrees Celsius) and the ceramic material 26. In the illustrated embodiment, the spacer 34 prevents the ceramic material 26 from entirely filling the bore 42 of the housing 22. In some low temperature applications, the spacer 34 can be eliminated, with the ceramic material 26 filling more of the bore 42. The ceramic material 26 also bonds to the weld ring 38 to support the weld ring 38 apart from the housing 22. The weld ring 38 provides a coupling area for the wire harness subassembly 18 as will be further described below.

[0010] In the illustrated construction, the sensor element 30 is a planar type sensor. Reference is made to U.S. Patent No. 6,164,120, for discussion of additional features and operations of the planar type sensor not described herein. The sensor element 30 has a first end 46 extending out from one end of the ceramic material 26 and a second end 50 extending out from the opposite end of the ceramic material 26. In the illustrated embodiment, the first end or exhaust side 46 of the sensor element 30 is surrounded by an inner protection tube 54 and an outer protection tube 58. The exhaust side 46 of the sensor element 30 is exposed to exhaust gas generated by the internal combustion engine.

[0011] The second end or reference side 50 of the sensor element 30 is surrounded by the wire harness subassembly 18 and is exposed to reference air from the environment. However, in other constructions (not shown), the ceramic material 26 may also encapsulate the reference side 50 of the sensor element 30 and an air channel is molded or formed (e.g., by drilling) in the ceramic material 26 to allow communication of the sensor element 30 with the reference air.

[0012] In the illustrated embodiment, four terminal pins or weld pins 62 electrically couple to the sensor element 30 by, for example, resistance welding or brazing. The ceramic material 26 partially encapsulates the terminal pins 62 such that one end of each terminal pin 62 extends from the ceramic material 26. The terminal pins 62 facilitate electrical contact between the wire harness subassembly 18 and the sensor element 30. In other embodiments, fewer or more terminal pins may be used.

[0013] The wire harness subassembly 18 includes signal wires 66, heater wires 70, a cap 74, a seal grommet 78, and a sleeve 82. Weld terminals 86 are positioned on each wire 66, 70 and electrically couple with the corresponding terminal pins 62 of the sensor subassembly 14 by resistance welding or other suitable alternatives. The illustrated wire harness subassembly 18 includes four wires 66, 70 and weld terminals 86. However, it should be readily apparent to one skilled in the art that the wire harness subassembly 18 could be modified to include fewer or more wires 66, 70 and weld terminals 86 to match the number of terminal pins 62 of the sensor subassembly 14.

[0014] The seal grommet 78 is positioned partially within a first end 90 of the sleeve 82 to support the wires 66, 70. The cap 74 secures the seal grommet 78 in place and couples to the first end 90 of the sleeve 82 by crimping or other suitable securing operations (e.g., brazing, welding, adhesives, etc.). The wire harness subassembly 18 couples to the weld ring 38 of the sensor subassembly 14 at a second end 94 of the sleeve 82 by press fitting and laser welding. Of course, other suitable securing operations may also be used.

[0015] The exhaust gas sensor 10 is manufactured by positioning the sensor subassembly 14, minus the ceramic material 26, within a mold cavity 98 of a mold fixture 102, as shown in Fig. 3. Liquefied or flowable ceramic material is injected (e.g., forced under pressure) into the mold cavity 98, overmolding a portion of the housing 22 and partially filling the bore 42 of the housing 22. The injected ceramic material also overmolds and partially surrounds the middle portion of the sensor element 30 and portions of the terminal pins 62. As the injected ceramic material cools, the ceramic material 26 hardens, thereby bonding to the housing 22. Also during hardening, the ceramic material 26 bonds to and encapsulates the middle portion of the sensor element 30 and portions of the terminal pins 62, forming a hermetic seal about the middle portion of the sensor element 30 and the terminal pins 62. The weld ring 38 is positioned in the mold cavity 98 apart from the housing 22 such that as the injected ceramic material cools, the ceramic material 26 also bonds to the weld ring 38. Once the ceramic material 26 hardens, the overmolded sensor subassembly 14 is removed from the mold cavity 98. The bonding of the ceramic material 26 to the housing 22, the sensor element 30, the terminal pins 62, and the weld ring 38 integrates the sensor subassembly 14 into a single, inseparable piece.

[0016] Fig. 4 illustrates the overmolded sensor subassembly 14 separated from the wire harness subassembly 18. After the overmolded sensor subassembly 14 is removed from the mold fixture 102, the inner protection tube 54 and the outer protection tube 58 are coupled to the housing 22 adjacent to the exhaust side 46 of the sensor element 30 by crimping, welding, or other suitable methods. The wire harness subassembly 18 components are assembled apart from the sensor subassembly 14, and are then coupled to the sensor subassembly 14 by first resistance welding the weld terminals 86 to the terminal pins 62 and then press fitting and laser welding the sleeve 82 to the weld ring 38.

[0017] The illustrated exhaust gas sensor 10 reduces the total number of components required for construction. For example, prior art exhaust gas sensors use steatite packing and boron nitride packing positioned about the middle portion of the sensor element to seal the reference side from the exhaust side. These packings are susceptible to characteristic shift downward (CSD) problems due to fuel vapor contamination. In the illustrated exhaust gas sensor 10, both the steatite packing and boron nitride packing are replaced by the ceramic material 26, which acts as a hermetic seal and is less susceptible to CSD.

[0018] In addition, the illustrated exhaust gas sensor 10 reduces the complexity and size of the manufacturing process required. Not only are the number of components required reduced, but the sensor element length may also be reduced compared to currently used exhaust gas sensors.

[0019] The illustrated exhaust gas sensor 10 also provides an insulating barrier between the metal components (e.g., the housing 22 and the sleeve 82) to prevent excess conduction of heat to sensitive components, such as the seal grommet 78 and the wires 66, 70. The ceramic material 26 is a highly insulative barrier that prevents the transfer of heat from the exhaust side 46 of the sensor element 30 to the reference side 50. The ceramic material 26 improves thermal operating characteristics of the exhaust gas sensor 10 by breaking the metal to metal contact and having a low thermal conductivity (about 0.8 W/m.K) compared to steatite bushings (about 1.6 W/m·K) or stainless steel (about 14 W/m·K).

[0020] Furthermore, the ceramic material 26 retains and isolates the terminal pins 62 to withstand high pull forces and vibrations. In other words, pull forces and vibrations that might otherwise cause separation between the sensor element 30 and the terminal pins 62 do not cause such separation in the illustrated exhaust gas sensor 10 due to the overmolded ceramic material 26.

Claims

1. A method of manufacturing an exhaust gas sensor (10) having a subassembly (14) including a housing (22), a sensor element (30), and a weld ring (38), the method comprising:

positioning at least a portion of the housing (22) and at least a portion of the sensor element (30) in a cavity (98) of a mold fixture (102);

positioning the weld ring (38) in the mold cavity (98) apart from the housing (22);

injecting a ceramic material (26) into the mold cavity (98) to overmold at least a portion of the housing (22) and at least a portion of the sensor element (30), and to mold the ceramic material (26) to the weld ring (38); and

removing the overmolded subassembly (14) from the mold fixture (102).

2. The method of claim 1, wherein injecting the ceramic material (26) at least partially encapsulates the sensor element (30).

3. The method of claim 2, wherein the subassembly (14) includes a terminal pin (62) electrically coupled to the sensor element (30), and the method further comprising coupling a wire (66, 70) to the terminal pin (62).

4. The method of claim 3, wherein injecting the ceramic material (26) at least partially encapsulates the terminal pin (62).

5. The method of claim 1, wherein injecting the ceramic material (26) results in bonding of the ceramic material (26) to the housing (22).

6. The method of claim 5, wherein the housing (22) includes a bore (42), and wherein injecting results in the ceramic material (26) at least partially filling the bore (42).

7. The method of claim 1, further comprising coupling a wire harness sleeve (82) to the weld ring (38).

8. The method of claim 7, wherein coupling the wire harness sleeve (82) to the weld ring (38) includes welding the wire harness sleeve (82) to the weld ring (38).

9. The method of claim 7, wherein the ceramic material (26) provides an insulating barrier between the housing (22) and the wire harness sleeve (82).

10. The method of claim 9, wherein the ceramic material (26) is a mica material.

11. An exhaust gas sensor assembly (10) comprising:

a housing (22);

a sensor element (30) partially received in the housing (22);

a ceramic material (26) molded to the housing (22) to encapsulate a portion of the sensor element (30); and characterised by

a weld ring (38) molded to the ceramic material (26) and spaced apart from the housing (22).

12. The exhaust gas sensor assembly (10) of claim 11, wherein the ceramic material (26) encapsulates a central portion of the sensor element (30), leaving at least one end of the sensor element (30) un-encapsulated.

13. The exhaust gas sensor assembly (10) of claim 11, wherein the ceramic material (26) is at least partially molded into a bore (42) in the housing (22).

14. The exhaust gas sensor assembly (10) of claim 11, further comprising a spacer (34) positioned in the housing (22), the ceramic material (26) abutting the spacer (34).

15. The exhaust gas sensor assembly (10) of claim 11, further comprising a wire harness subassembly (18), the wire harness subassembly (18) including a wire (66, 70) and a sleeve (82).

16. The exhaust gas sensor assembly (10) of claim 15, wherein the sleeve (82) of the wire harness subassembly (18) is coupled to the weld ring (38).

17. The exhaust gas sensor assembly (10) of claim 15, further comprising a terminal pin (62) having a first end electrically coupled with the sensor element (30), wherein the terminal pin (62) is at least partially encapsulated by the ceramic material (26) such that a second end of the terminal pin (62) extends from the ceramic material (26) and couples to the wire (66, 70) of the wire harness subassembly (18).

18. The exhaust gas sensor assembly (10) of claim 11, wherein the sensor element (30) is a planar sensor element.

19. The exhaust gas sensor assembly (10) of claim 11, wherein the molded ceramic material (26) is a mica material.

20. The exhaust gas sensor assembly (10) of claim 16, wherein the sleeve (82) of the wire harness subassembly (18) is welded to the weld ring (38).

21. The exhaust gas sensor assembly (10) of claim 16, wherein the ceramic material (26) provides an insulating barrier between the housing (22) and the sleeve (82) of the wire harness subassembly (18).

22. The exhaust gas sensor assembly (10) of claim 21, wherein the ceramic material (26) is a mica material.

Ansprüche

1. Herstellungsverfahren für einen Abgassensor (10) mit einer Untergruppe (14) einschließlich eines Gehäuses (33), eines Sensor-Elementes (30) und eines Schweißringes (38), wobei das Verfahren folgendes aufweist:

Positionieren mindestens eines Teils des Gehäuses (22) und mindestens eines Teils des Sensor-Elementes (30) in einem Hohlraum (98) einer Form-Haltevorrichtung (102);

Positionieren des Schweißringes (38) in dem Hohlraum der Form (98) getrennt vom Gehäuse (22);

Einspritzen von keramischem Material (26) in den Hohlraum der Form (98), um mindestens einen Teil des Gehäuses (22) und einen Teil des Sensor-Elementes (30) zu umspritzen, und das keramische Material (26) an den Schweißring (38) zu formen; und

Entfernen der umspritzten Untergruppe (14) aus der Form-Haltevorrichtung (102).

2. Verfahren nach Anspruch 1, wobei das Sensor-Element (30) durch das Einspritzen des keramischen Materials (26) mindestens teilweise eingekapselt wird.

3. Verfahren nach Anspruch 2, wobei die Untergruppe (14) einen Anschluss-Stift (62) aufweist, der mit dem Sensor-Element (30) elektrisch verbunden ist, und das Verfahren weiterhin darin besteht, dass ein Kabel (66,70) mit dem Anschluss-Stift (62) verbunden wird.

4. Verfahren nach Anspruch 3, wobei der Anschluss-Stift (62) durch das Einspritzen des keramischen Materials (26) mindestens teilweise eingekapselt wird.

5. Verfahren nach Anspruch 1, wobei das Einspritzen des keramischen Materials (26) dazu führt, dass das keramische Material (26) durch Bonden mit dem Gehäuse (22) verbunden wird.

6. Verfahren nach Anspruch 5, wobei das Gehäuse (22) eine Bohrung (42) aufweist, und wobei die Bohrung (42) durch das Einspritzen mindestens teilweise mit dem keramischen Material (26) gefüllt wird.

7. Verfahren nach Anspruch 1, das weiterhin darin besteht, eine Kabelsatz-Muffe (82) mit dem Schweißring (38) zu verbinden.

8. Verfahren nach Anspruch 7, wobei das Verbinden der Kabelsatz-Muffe (82) mit dem Schweißring (38) das Verschweißen der Kabelsatz-Muffe (82) mit dem Schweißring (38) einschließt.

9. Verfahren nach Anspruch 7, wobei das keramische Material (26) eine Isolierbarriere zwischen dem Gehäuse (22) und der Kabelsatz-Muffe (82) liefert.

10. Verfahren nach Anspruch 9, wobei es sich bei dem keramischen Material (26) um einen Glimmerwerkstoff handelt.

11. Abgassensor-System (10) mit:

einem Gehäuse (22);

einem Sensor-Element (30), das teilweise in dem Gehäuse (22) untergebracht ist;

einem keramischen Material (26), das an das Gehäuse (22) geformt ist, um einen Teil des Sensor-Elementes (30) einzukapseln; und gekennzeichnet durch

einen Schweißring (38), der an das keramische Material (26) geformt ist, und zu dem Gehäuse (22) beabstandet ist.

12. Abgassensor-System (10) nach Anspruch 11, wobei ein mittlerer Abschnitt des Sensor-Elementes (30) durch das keramische Material (26) eingekapselt wird, und mindestens ein Ende des Sensor-Elementes (30) uneingekapselt bleibt.

13. Abgassensor-System (10) nach Anspruch 11, wobei das keramische Material (26) mindestens teilweise in eine Bohrung (42) in dem Gehäuse (22) geformt wird.

14. Abgassensor - System (10) nach Anspruch 11, das weiterhin einen Abstandhalter (34) aufweist, der in dem Gehäuse (22) positioniert ist, wobei das keramische Material (26) an den Abstandhalter (34) anstößt.

15. Abgassensor-System (10) nach Anspruch 11, das weiterhin eine Kabelsatz-Untergruppe (18), die Kabelsatz-Untergruppe (18) mit einem Kabel (66, 70) und eine Muffe (82) aufweist.

16. Abgassensor-System (10) nach Anspruch 15, wobei die Muffe (82) der Kabelsatz-Untergruppe (18) mit dem Schweißring (38) verbunden ist.

17. Abgassensor-System (10) nach Anspruch 15, das weiterhin einen Anschluss-Stift (62) aufweist, dessen erstes Ende mit dem Sensor-Element (30) elektrisch verbunden ist, wobei der Anschluss-Stift (62) mindestens teilweise durch das keramische Material (26) eingekapselt ist, so dass sich ein zweites Ende des Anschluss-Stiftes (62) von dem keramischen Material (26) aus erstreckt und sich mit dem Kabel (66, 70) der Kabelsatz-Untergruppe (18) verbindet.

18. Abgassensor-System (10) nach Anspruch 11, wobei es sich bei dem Sensor-Element (30) um ein planares Sensor-Element (30) handelt.

19. Abgassensor-System (10) nach Anspruch 11, wobei es sich bei dem geformten keramischen Material (26) um einen Glimmerwerkstoff handelt.

20. Abgassensor-System (10) nach Anspruch 16, wobei die Muffe (82) der Kabelsatz-Untergruppe (18) mit dem Schweißring (38) verschweißt ist.

21. Abgassensor-System (10) nach Anspruch 16, wobei das keramische Material (26) eine Isolierbarriere zwischen dem Gehäuse (22) und der Muffe der Kabelsatz-Untergruppe (18) liefert.

22. Abgassensor-System (10) nach Anspruch 21, wobei es sich bei dem keramischen Material (26) um einen Glimmerwerkstoff handelt.

Revendications

1. Procédé de fabrication d'un capteur de gaz d'échappement (10) possédant un sous-ensemble (14) incluant un boîtier (22), un élément de capteur (30), et une bague à souder (38), le procédé comprenant :

le positionnement d'au moins une portion du boîtier (22) et d'au moins une portion de l'élément de capteur (30) dans une cavité (98) d'un moule (102) ;

le positionnement de la bague à souder (38) dans la cavité de moule (98) séparément du boîtier (22) ; l'injection d'un matériau de céramique (26) dans la cavité de moule (98) pour surmouler au moins une portion du boîtier (22) et au moins une portion de l'élément de capteur (30) et pour mouler le matériau de céramique (26) sur la bague à souder (38) ; et

l'enlèvement du sous-ensemble surmoulé (14) du moule (102).

2. Procédé selon la revendication 1, dans lequel l'injection du matériau de céramique (26) enrobe au moins partiellement l'élément de capteur (30).

3. Procédé selon la revendication 2, dans lequel le sous-ensemble (14) inclut une broche borne (62) couplée électriquement à l'élément de capteur (30), et le procédé comprenant en outre le couplage d'un fil (66, 70) avec la broche borne (62).

4. Procédé selon la revendication 3, dans lequel l'injection du matériau de céramique (26) enrobe au moins partiellement la broche borne (62).

5. Procédé selon la revendication 1, dans lequel l'injection du matériau de céramique (26) entraîne la liaison du matériau de céramique (26) et du boîtier (22).

6. Procédé selon la revendication 5, dans lequel le boîtier (22) inclut un alésage (42), et dans lequel l'injection entraîne que le matériau de céramique (26) remplit au moins partiellement l'alésage (42).

7. Procédé selon la revendication 1, comprenant en outre le couplage d'un manchon de faisceau électrique (82) avec la bague à souder (38).

8. Procédé selon la revendication 7, dans lequel le couplage du manchon de faisceau électrique (82) avec la bague à souder (38) inclut le soudage du manchon de faisceau électrique (82) et de la bague à souder (38).

9. Procédé selon la revendication 7, dans lequel le matériau de céramique (26) fournit une barrière isolante entre le boîtier (22) et le manchon de faisceau électrique (82).

10. Procédé selon la revendication 9, dans lequel le matériau de céramique (26) est du mica.

11. Ensemble de capteur de gaz d'échappement (10) comprenant :

un boîtier (22) ;

un élément de capteur (30) partiellement reçu dans le boîtier (22) ;

un matériau de céramique (26) moulé sur le boîtier (22) pour enrober une portion de l'élément de capteur (30) ; et caractérisé par

une bague à souder (38) moulée sur le matériau de céramique (26) et séparée du boîtier (22).

12. Ensemble de capteur de gaz d'échappement (10) selon la revendication 11, dans lequel le matériau de céramique (26) enrobe une portion centrale de l'élément de capteur (30), en laissant au moins une extrémité de l'élément de capteur (30) non enrobé.

13. Ensemble de capteur de gaz d'échappement (10) selon la revendication 11, dans lequel le matériau de céramique (26) est au moins partiellement moulé dans un alésage (42) du boîtier (22).

14. Ensemble de capteur de gaz d'échappement (10) selon la revendication 11, comprenant en outre une entretoise (34) positionnée dans le boîtier (22), le matériau de céramique (26) butant contre l'entretoise (34).

15. Ensemble de capteur de gaz d'échappement (10) selon la revendication 11, comprenant en outre un sous-ensemble de faisceau électrique (18), le sous-ensemble de faisceau électrique (18) incluant un fil (66, 70) et un manchon (82).

16. Ensemble de capteur de gaz d'échappement (10) selon la revendication 15, dans lequel le manchon (82) du sous-ensemble de faisceau électrique (18) est couplé avec la bague à souder (38).

17. Ensemble de capteur de gaz d'échappement (10) selon la revendication 15, comprenant en outre une broche borne (62) ayant une première extrémité couplée électriquement avec l'élément du capteur (30), dans lequel la broche borne (62) est au moins partiellement enrobée par le matériau de céramique (26) de telle sorte qu'une seconde extrémité de la broche borne (62) s'étend à partir du matériau de céramique (26) et est couplée avec le fil (66, 70) du sous-ensemble de faisceau électrique (18).

18. Ensemble de capteur de gaz d'échappement (10) selon la revendication 11, dans lequel l'élément de capteur (30) est un élément de capteur plan.

19. Ensemble de capteur de gaz d'échappement (10) selon la revendication 11, dans lequel le matériau de céramique moulé (26) est du mica.

20. Ensemble de capteur de gaz d'échappement (10) selon la revendication 16, dans lequel le manchon (82) du sous-ensemble de faisceau électrique (18) est soudé sur la bague à souder (38).

21. Ensemble de capteur de gaz d'échappement (10) selon la revendication 16, dans lequel le matériau de céramique (26) fournit une barrière isolante entre le boîtier (22) et le manchon (82) du sous-ensemble de faisceau électrique (18).

22. Ensemble de capteur de gaz d'échappement (10) selon la revendication 21, dans lequel le matériau de céramique (26) est du mica.

Drawing